IMPROVED FOAMING BEHAVIOUR OF POLYMER COMPOSITIONS USING BLOWING AGENT AND NUCLEATION AGENT
The invention relates to a foamable polymer composition comprising a blowing agent and a foamed polymer composition obtained by foaming this foamable polymer composition. The invention further relates to a cable comprising at least one layer which comprises the foamable polymer composition or a foamed polymer composition.
1 . Foamable polymer composition comprising
(A) a first polyolefin polymer,
(B) a second polyolefin polymer having an MFR 2 (2.16 kg; 190° C.) of 2 to 15 g/10 min measured according to ISO 1133, and
(C) a blowing agent in an amount of 0.01 wt. % to 2 wt. % based on the total foamable polymer composition,
wherein the blowing agent (C) comprises citric acid and/or derivative of citric acid in an amount of more than 90 wt. % based on the total blowing agent (C), and
wherein the first polyolefin polymer (A) has a higher density than the second polyolefin polymer (B).
2 . The foamable polymer composition according to claim 1 , wherein the derivative of citric acid comprises alkali metal salts of citric acid, esters of citric acid or mixtures thereof.
3 . The foamable polymer composition according to claim 1 , wherein the foamable polymer composition further comprises a mineral nucleating agent (E).
4 . The foamable polymer composition according to claim 1 , wherein the first polyolefin polymer (A) has an MFR 2 (2.16 kg; 190° C.) of 0.1 to 20 g/10 min measured according to ISO 1133.
5 . The foamable polymer composition according to claim 1 , wherein the first polyolefin polymer (A) is present in amount of 20 to 95 wt. % based on the total foamable polymer composition and wherein the second polyolefin polymer (B) is present in an amount of 5 to 80 wt. % based on the total foamable polymer composition.
6 . The foamable polymer composition according to claim 1 , wherein the first polyolefin polymer (A) is a high density polyethylene homo- or copolymer having a density of 935 kg/m 3 to 970 kg/m 3 measured according to ISO 1183-1 and the second polyolefin polymer (B) is a low density polyethylene homopolymer having a density of 880 kg/m 3 to 930 kg/m 3 measured according to ISO 1183-1.
7 . The foamable polymer composition according to claim 1 , wherein the foamable polymer composition has a dissipation factor at 1.9 GHz of 80·10 −6 to 160 0·10 −6 and/or a dissipation factor at 1 MHz of 20·10 −6 to 140 0·10 −6 .
8 . Foamed polymer composition obtained by foaming the foamable polymer composition according to claim 1 .
9 . Foamed polymer composition according to claim 8 , wherein foaming is done by heating the foamable polymer composition to a temperature of 150° C. to 240° C.
10 . Foamed polymer composition according to claim 8 , wherein a co-blowing agent (D) is added to the foamable polymer composition.
11 . Foamed polymer composition according to claim 10 , wherein the co-blowing agent (D) comprises N 2 , CO, CO 2 , Ar or mixtures thereof.
12 . Foamed polymer composition according to claim 10 , wherein the co-blowing agent (D) is used in amount of 0.01 wt. % to 0.5 wt. % based on the total foamable polymer composition.
13 . Foamed polymer composition according to claim 8 , wherein the foamed polyolefin composition has a mean cell diameter of 5 μm to 250 μm.
14 . The foamed polymer composition according to claim 8 , wherein the foamed polymer composition has a density of 95 kg/m 3 to 860 kg/m 3 .
15 . Cable comprising at least one layer which comprises the foamable polymer composition according to claim 1 .
16 . Cable comprising at least one layer which comprises the foamed polymer composition according to claim 8 .